Question

ab+ac+a=165
b+c=10
a=?

Answer 1

ab+ac+a = a(b+c+1)
a(b+c+1) =165
a(10+1) = 165
11a = 165   |:11
a = 15

Answer 2

$ab+ac+a=165 \\ b+c=10 \\ ab+ac+a=165 \\ a(b+c)+a=165 \\ 10a+a=165 \\ 11a=165 \\ a=165:11 \\ \boxed{a=15}$